Intercommunicating apparatus



Patented Aug. 12, 1952 INTERCOMMUNIGATING APPARATUS Richard H. Campbell, Racine, Wis., assignor to Webster Electric Company, Racine, Wis., a corporation of Delaware Application March 26, 1948, Serial No. 17,155

13 Claims.

The present invention relates to intercommunicating apparatus and has for its primary ob-' ject the provision of. new and improved apparatus of this character and a system including such apparatus. 1 I

One of the objects of the present invention is to provide a new, improved, and simplified loudspeaking intercommunicating system utilizing munication control switch, and one or more other stations, each including electroacoustioal translating means, andwherein each of the latter stations may call the master station, even when the latter is communicating with another of the said other stations.

A further object of the present invention is the provision of .new and improved communicating apparatus comprising a plural position communication control switch'and visual means adapted to indicatedifierent positions of. the switch.

Another-object of "the present invention is the provision of new and improved intercommunicating -=apparatus adapted to be supplied with power through a rectifier having resistance means at its input side for supplying added filter action, acting as a fuse under certain conditions and as a peak charging current'lhniter and, still further, cooperating with resistance means controlled by a multiple position communication control switch to provide a reduced-output voltag in certain positions of the switch. I I

Other objects andadvantages .of the present invention will become apparent from the .ensuing description of an embodimentxthereof, in the course of which reference is had .to the accompanying drawing, thesinglefigure ofswhich is a schematic representation of .annapparatus and system embodying the invention.

Referring now. to the drawing, the present invention is illustrated in connection with a system including "a .first station, indicated by the reference character l, which is a master station, and

two other stations 2 and-3,,located :atadistance from the first stat-ion and which'willhereinafter be called remote zor: substations. The system is so constructed and arranged that the remote stations 2 and 3 can call the master station and that th master station can call the remote stations and control the direction of communication between the stations.

The master station includes an amplifier l0 comprising an input transformer 12 and an output transformer l4 interconnected by tubes 16 and [8, which may be of known type and connected in known manner. Power issupplied to th amplifier from either an A. C. or D. C. source through rectifying means including a tube 20.

The three stations illustrated are each provided with electroacoustical translating means which may be loud-speakers 2 I, 22' and 23 located at stations I, 2 and 3, respectively. The master station is also provided with a Communication direction and amplifierpower supply controlling switch, indicated as a whole by reference character 24. It is also provided with station selector switch means 25 and the remote stations are provided with call-in switcheS 25C.

The communication direction and amplifier power. supply controlling switch 24 is operable into a plurality of positions. These are a listen position, in which the switch is indicated, a talk position, which is one position downwardly from that indicated, and an idle position. which-is one position upwardly from that indicated. In the idle position, the supply of plate voltage from the rectifier to the amplifier is discontinued but the other-two positions the amplifier issupplied with plate voltag and is Operative. In the listen position, the loud-speaker 2i is connected to the output of the amplifier, whil a. communication circuit comprising conductors 26 and 28, the latter of which is, in accordance-With one of the features of the present invention, ungrounded common conductor for the loud-Smkersand for the amplifier input and output, is connected to the input of the ampl fier. The connection to the output of the amplifying means is effected through'a secondary winding 30 of th output transformerl4, while the connection to the input is effected through the primary winding 32 of the input transformer l2. 1

The u'seof an ungrounded-commonlme the advantage that he number of contacts on the communication direction control switch 24 can be reduced, as only one side of the communication circuit .hasto be switched, and yet the communication circuitis substantially balanced with the result that cross talk, noise and hum are minimiZed. 1

In the indicated listen position of the switch, the loud-speaker 2| is connected to the secondary winding 38 of the output transformer and the communication circuit 26, 28 is connected to the primary winding 32 of the input transformer. The connection of the loud-speaker to winding 38 is effected through the common conductor 28, which connects one terminal of the transformer to one terminal of the loud-speaker coil, and through conductor 34, switch blades 36 and 38 of switch 24, and conductor 40. Th communication circuit 26, 28 is connected to the input transformer primary winding 32 through the common conductor 28 and through conductor 42, switch blade 44 of switch 24, and conductor 48.

In the talk position of switch 24, the connections of the communication circuit 25, 28 and of the loud-speaker 2| to the amplifier are reversed. The loud-speaker is connected to the input of the amplifier through the previously mentioned conductor 28, conductor 48, switch blades 36 and 88, and conductor 48. The communication circuit is connected to the output of the amplifier through the common conductor 28 and through conductor 42, switch blade 44, and conductor 34.

In order to minimize feedback from the output to the input of the amplifier, a resistor 48 is connected across the input and the secondary winding 38 of the output transformer I4 is so phased relative to the input that they are in phase opposition at higher frequencies passed by the amplifier. The resistor 48 loads the input transformer and prevents a phase shift that could result in feedback (oscillation) of the amplifier. The feedback is also reduced by a shield 50 between the primary and secondary windings of the input transformer and which is connected to ground (the chassis of the unit) by conductor 52. The resistor 48 also limits the primary impedance and therefore minimizes noise and hum pickup between interstation wires.

The station selector switch 25 is adapted selectively to connect the communication circuit 26, 28 to the remote stations 22 and 23. The selector switch 25 includes two switch blades 56 and 58 connected, respectively, to conductors 26 and 28. Each blade is operable to engage a plurality of contacts which may be connected by interstation conductors to the remote stations. In order to simplify the present description, only the two stations 2 and 3 have been illustrated. The former is connected by conductors 68 and 82 to corresponding contacts associated with switch blades 56 and 58. Station 3 is similarly connected by conductors 64 and 66 to the corresponding contacts of the two switch blades. In the indicated position of the selector switch, station 3 is shown selected, the switch blades 58 and 58 connecting conductors26 and 28 to conductors 64 and 86, respectively.

In accordance with another feature of the present invention, the remote stations can call the master station even though the selector switch 58 is left in position to select a particular station. The'remote stations can call the master station through a call-in circuit comprising conductors S8 and connected to corresponding contacts associated with switches 56 and 58 of the selector switch 25. To condition the master station for call in by remote stations, the switch blades 56 and'58 would normally be operated to complete the circuit to conductors 68 and 18, but even though this not be done, the circuit is completed at all times by jumper conductors 1'2 and 14 connecting the switch blades 56 and 58 directly to conductors 28 and 28.

When the remote station desires to call the master station (and this is done when the switch. 24 at the master station is in its listen position) all that is necessary is the closure of the call-in switch 250, thereby to connect the associated loud-speaker to the call-in circuit and thence to the input of the amplifier as previously described.

Other features of the present invention reside in the control of the plate voltage supply and in means for indicating the various positions of the switch 24.

The communication direction and power supply controlling switch 24 is constructed and arranged to complete the plate voltage supplying circuit to the rectifier 28 in the listen and talk positions. The rectifier is conditioned to be ready for operation as are the tubes [6 and i8 of the amplifier upon the completion of the rectifier plate voltage supply circuit. The tubes 16 and I8 are permanently connected to the output of the rectifier and all three tubes have their filaments connected in series across the power supply by conductors 18 and 18. Thus, the amplifier is rendered operative whenever the plate voltage connection to the rectifier is completed and this connection is completed by switch blade 88 of switch 24 in the listen and talk positions of the latter. In the listen position, the rectifier plate voltage circuit is completed through a pilot light 82, which serves a number of functions as will be brought out hereinafter, resistor 84, conductor 86, switch blade 80, resistor 88, and conductor 99.

The resistor 84, in accordance with another feature of the present invention, cooperates with resistor 88 to provide a reduced plate voltage to the amplifier tubes in the listen position. The resistor 84 is also designed to act as a fuse in the case of short circuits and it also acts as a peak charging current limiter whenever the rectifier is placed into operation and prevents the pilot light 84 from being supplied with too high a cur rent upon initial closure of the plate voltage circuit. In the talk position of switch 24, the switch blade interconnects conductors 86 and and thus eliminates resistor 88 from the circuit so that a higher plate voltage is supplied to the rectifier and the latter thus supplies a higher plate voltage to tubes 16 and Hi. The result is transmission at a higher level than reception.

The pilot light 82 indicates the positions of the switch 24. In the idle position of the switch, a low value of current flows through the light, the pilot light being connected from conductor 12 to the midpoint of the cathode heater or filament 92 of the rectifier tube 20 by a conductor 94. In the listen position of switch 24, a greater current flows through the pilot light because the plate current flows through it. At this time resistors 84 and 88 are in circuit with the pilot light so that a lower value of current flows through it than when the switch 24 is in its talk position. In the talk position, the light glows with its greatest brilliancy as the plate current is greater.

The operation of the system as a wholewill now be reviewed, it being assumed that the conductors 16 and l8'are connected to a suitable source of power, which may be eitheralternating or'direct current; When thus connected, the cathode heaters are all energized, they being connected in series across the power line. The pilot light 82 glows with a brilliancy dependent upon the position of the communication'direction and power controlling switch 24." Assuming first that the latter is .in idle position. the pilot light glows with its lowest .brilliaiicyg' Assuming now that the masterstation desires to communicate with station 3, the station selector switch -25 .is operated to its indicated position. The switch 24 is operated to, its talk'position andthe master station can then call the remote station, the loud-speaker .2] being connected to the input and the loud-speaker 23 being connected to the output of the amplifier. The pilot light glows'with its greatest brilliancy because resistor 88 is eliminatedfrom the rectifier circuit. To receive from .station 3, the-talk-listen switch is returned to its listen position, which is ordinarily done simply upon releaseof the. switch by a spring biasing it from its talk to its listen position.

v,Aft'er completion of the call, the selector switch 25 is returned to interconnect conductors .26 and 28 with the call-in circuit conductors 68=and 10. However, even though this not be done, a remote station can .call the master station,.assumi-ng that the latter. leaves the switch 24 in itslisten'position. All that is necessary fora remote station ,to call the master station is theclosure of switch 25C, whereby the loud-speaker at the remote station is connected to the input of the amplifier, the loud-speaker 2| at the master station being connected to the output of the amplifier.

The apparatus of the present invention has a number of advantages. The use of an ungrounded common conductor reduces the number of switches and yet provides a substantially balanced line. Feedback and the pick-up of noise is minimized by the shield 50, the resistor 48, and the phasing of the primary and secondary windings of the input and output transformers, respectively. Another advantage is that the position of the switch24 is indicated by the pilot light. This-is of particular advantage to a serviceman who might be checking the operation of the apparatus. Also, the remote station can call in the .master station even though theselector switch 25 not be returned to a particular position. Furthermore, the plate voltage supply is. controlled in a, novel manner and includes the resistor 84 performing a number of functions as heretofore indicated.

While the present inventionhas been described in connection with the details of an illustrative embodiment thereof, it should .be understood that these details are not intended to be limitative of the invention, except in so far as set forth in the accompanying claims.

Having thus described my invention, what I claim as new and desire to secure .by Letters Patent of the United States is:

1. A communication system including a first station having amplifying means with input and output circuits, electroacoustical translating means, a second station having electroacoustical translating-means, and means comprising circuits including an ungrounded twowire interstation circuit, of which one wire is common to both said means and to the amplifier-input andoutput circuits and is permanently connected to said first mentioned translating means and said input and output circuits, and communication control switch means at said first station for selectively connecting said translating means to the input and output circuits of said amplifier means.

2. A communication system including a first station having audio frequency amplifying means with input and output circuits, said input and output circuits including transformers and the v secondary-of the output transformer. being. so phased in relation to the primary ofj'the' jinputtransformer that they are in phasefiopposition at the higher .frequencies, 1 passed I by; the amplifier, electroacouslticall[translating means, a second .station having electroacoustical translatin means, and means comprisingmircuits. including an ungrounded two Jwireintersltation.circuit, of which one wire is common to both said translating means and tothe amplifierii'nput and out,- put circuits, and is, permanen'tlyv Leo nected to said "first mentioned translating 'm'eans, and to said transformers in said ifipllt; and output circuits and commuriicationlcontrot su'rit'ch, means at said first station for, selec'trelygconnectin said translating mean'sjlto the nput and output circuits .of said amplifying means... II L i f .3. A communicationasystem ehi'ding a first station having amplifying m I, thjinputan'd output circuits, said input .fcircui iincluding a transformer .and .a resistor eonnectea across the primary of said transformer, electroacoustical translating means, a .second'station having electroacoustical translating means, and means comprising circuits including ungrounded'twowire interstation circuit, oiwhich onejwireis. common to both said translatingemeans 'a'nd to theiamplifier input and outputcircuits andfis permanent ly connected to said .firstmentioi md translating means and to said transformers in .saidfinpu-tland output circuits, and communication control switch means at said first station for selectively connecting said translatingmeans to the'input and output circuits of saidgamlplifyingmeansif 4. A communication systemlir'icluding a first station having audio frequent; amplifying means with input and outputcirchi ,saidinput and output circuits including transformers. and the secondary of output r'rsusfrsrm epemg. o phased in relationto 'theipri'mary otthe' input transformer that the are, n. phase. .opposition at the higher frequenciespass'e ,ay theamplifier, a resistor connected across the trimmer: said input transformer, electroacoust'ical. translating including an. ungrounded two .iwire interstation circuit, of which one; wir s}. common to both said translating means audio-the amplifier input and output circuits, an communication control switch means at said M station for .selectively connecting-said-transla ng to the input and output o aidampiifying means.

5. A communication system including .a first station having amplifying-meanswithinput and output circuits, electroacoustical translating means, a plurality of .other stationseach having .electroacoustical translating means, means ,comprising circuits includmga twowire interstation circuit for each of said-otherstations and a two wire circuit .at thefirst station, of which circuits one wire is common to; bothaid translating means and to the amplifier inp nd-output circuits, and communication ontro witch rneans at Said. first station tor -s ecvely connecting-"said nently connected to and extending from the two wire circuit at said one station to said other stations, and switch means at each, of said other stations for connecting the electroacoustical call in circuit.

translating means at said other stations to its 6. Intercommunicating apparatus including amplifying means, a source ofpower for said amplifying means, electroacoustical translating means, a plural position communication control switch means and control circuits associated with said amplifying and translating means controlled by said switch means for controlling the connection of said translating means to said amplifying means, a pilot light, and means includingplural position switch means operable with said communication control switch means and associated with said power source and pilot light controlling circuits controlledby said last mentioned switch means for supplying said light with different amounts of power to cause it to glow with different brilliancies in difierent positions of said communication control switch.

7. Intercommunicating. apparatus including amplifying means, a source of power for said amplifying means, electroacoustical translating means, a three position communication control switch means and control circuits associated with said amplifying and translating means controlled by said switch means for controlling the connection of said translating means to said amplifying means, a pilot light, and means including three position switch means operable with said communication control switch means and associated with said power source andpilot light controlling circuits controlled by said last mentioned switch means for supplying said light with three different amounts of power to cause it to glow with three difierent brilliancies in different positions of said communication control switch.

8. Intercommunicating apparatus including amplifying means, a source of power including rectifying means for said amplifying means, electroacoustical translating means, a three position communication control switch means and control circuits associated with said amplifying and translating means controlled by said switch means for connecting said translating means to the input or output of or disconnecting it from said amplifying means, a pilot light, and means including a three position switch means'connected to said communication control switch means and associated'with said rectifying means and pilot light controlling circuits including resistance means controlled by said last mentioned switch means for supplying said light with three different amounts of power to cause it to glow with three different brilliancies in different positions of said communication control switch.

9. Intercommunicating apparatus of the type including amplifying means, comprising a rectifier connected to said amplifying means, and means including switch means and a series resistor at the input side of said rectifier controlling the power input connections of said rectifier.

10. Intercommunicating apparatus including amplifying means, a rectifier connected to said amplifying means, and means including a series resistor, a multiple position communication controlling switch associated with said amplifying means, and additional resistance means insertable in series with said resistor in one position of said switch for controlling the input connections of saidrectifier.

11. An intercommunicating system including a first station having amplifying means including input and output circuits, electroacoustical translating means, a communication circuit, and switch means associated with said amplifying means and translating means for connecting said communication circuit and translating means to the input and output circuits, respectively, of said amplifying means, a second station including electroacoustical translating means, interstation communication and call-in circuits connecting said last mentioned translating means to said first station, station selector switch means at said first station associated with both said communication circuits for connecting them, and a circuit permanently connecting said call-in circuit to the communication circuit at said first station.

' 12. An intercommunicating system including a first station having amplifying means including input and output circuits, electroacoustical translating means, a communication circuit, and switch means associated with said ampifying means and translating means for connecting said communication circuit and translating means to the input and output circuits, respectively, of said ampilfying means, a plurality of other stations including electroacoustical translating means, interstation communication and call-in circuits connecting said last mentioned translating means to said first station, a plural position station selector switch at said first station associated with said communication circuit and said interstation circuits for selectively connecting them, said call-in circuits all extending to one position of said selector switch, and a jumper circuit permanently connecting said call-in circuits to the communication circuit at said first station.

13. Intercommunicating apparatus including plural position communication control switch REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,107,817 Davis Feb. 8, 1938 2,162,369 Campbell June 13, 1939 2,162,370 Campbell June 13, 1939 2,269,144 Campbell Jan. 6, 1942 2,275,406 Berkley Mar. 10, 1942 2,326,616

Campbell Aug; 10, 1943 

